Skip to main content

Desgin Patterns

 Design Patterns.

1. Creational

2. Structural

3. Behavourial

In Behvorial

1. Strategy pattern

Example :

Step 1

Create an interface.

Strategy.java

public interface Strategy {
   public int doOperation(int num1, int num2);
}

Step 2

Create concrete classes implementing the same interface.

OperationAdd.java

public class OperationAdd implements Strategy{
   @Override
   public int doOperation(int num1, int num2) {
      return num1 + num2;
   }
}

OperationSubstract.java

public class OperationSubstract implements Strategy{
   @Override
   public int doOperation(int num1, int num2) {
      return num1 - num2;
   }
}

OperationMultiply.java

public class OperationMultiply implements Strategy{
   @Override
   public int doOperation(int num1, int num2) {
      return num1 * num2;
   }
}

Step 3

Create Context Class.

Context.java

public class Context {
   private Strategy strategy;

   public Context(Strategy strategy){
      this.strategy = strategy;
   }

   public int executeStrategy(int num1, int num2){
      return strategy.doOperation(num1, num2);
   }
}

Step 4

Use the Context to see change in behaviour when it changes its Strategy.

StrategyPatternDemo.java

public class StrategyPatternDemo {
   public static void main(String[] args) {
      Context context = new Context(new OperationAdd());		
      System.out.println("10 + 5 = " + context.executeStrategy(10, 5));

      context = new Context(new OperationSubstract());		
      System.out.println("10 - 5 = " + context.executeStrategy(10, 5));

      context = new Context(new OperationMultiply());		
      System.out.println("10 * 5 = " + context.executeStrategy(10, 5));
   }
}

Step 5

Verify the output.

10 + 5 = 15
10 - 5 = 5
10 * 5 = 50


2. Null Object Pattern

In Null Object pattern, a null object replaces check of NULL object instance. Instead of putting if check for a null value, Null Object reflects a do nothing relationship. Such Null object can also be used to provide default behaviour in case data is not available.
In Null Object pattern, we create an abstract class specifying various operations to be done, concrete classes extending this class and a null object class providing do nothing implemention of this class and will be used seemlessly where we need to check null value.
Implementation
We are going to create a AbstractCustomer abstract class defining opearations. Here the name of the customer and concrete classes extending the AbstractCustomer class. A factory class CustomerFactory is created to return either RealCustomer or NullCustomer objects based on the name of customer passed to it.
NullPatternDemo, our demo class, will use CustomerFactory to demonstrate the use of Null Object pattern
Example
Step 1
Create an abstract class.
AbstractCustomer.java
public abstract class AbstractCustomer {
   protected String name;
   public abstract boolean isNil();
   public abstract String getName();
}
Step 2
Create concrete classes extending the above class.
RealCustomer.java
public class RealCustomer extends AbstractCustomer {

   public RealCustomer(String name) {
      this.name = name;		
   }
   
   @Override
   public String getName() {
      return name;
   }
   
   @Override
   public boolean isNil() {
      return false;
   }
}
NullCustomer.java
public class NullCustomer extends AbstractCustomer {

   @Override
   public String getName() {
      return "Not Available in Customer Database";
   }

   @Override
   public boolean isNil() {
      return true;
   }
}

Step 3
Create CustomerFactory Class.
CustomerFactory.java
public class CustomerFactory {
	
   public static final String[] names = {"Rob", "Joe", "Julie"};

   public static AbstractCustomer getCustomer(String name){
   
      for (int i = 0; i < names.length; i++) {
         if (names[i].equalsIgnoreCase(name)){
            return new RealCustomer(name);
         }
      }
      return new NullCustomer();
   }
}
Step 4
Use the CustomerFactory to get either RealCustomer or NullCustomer objects based on the name of customer passed to it.
NullPatternDemo.java
public class NullPatternDemo {
   public static void main(String[] args) {

      AbstractCustomer customer1 = CustomerFactory.getCustomer("Rob");
      AbstractCustomer customer2 = CustomerFactory.getCustomer("Bob");
      AbstractCustomer customer3 = CustomerFactory.getCustomer("Julie");
      AbstractCustomer customer4 = CustomerFactory.getCustomer("Laura");

      System.out.println("Customers");
      System.out.println(customer1.getName());
      System.out.println(customer2.getName());
      System.out.println(customer3.getName());
      System.out.println(customer4.getName());
   }
}
Step 5
Verify the output.
Customers
Rob
Not Available in Customer Database
Julie
Not Available in Customer Database
3. State Pattern

Another Example
public class ReceiptStateActivity implements Processor {
event = ReceiptRulesState.start(receipt);
}
public class ReceiptRulesState
  extends AbstractRulesState<Receipt, Order, ReceiptStateResponseEvent, ReceiptStateResponseEvent> {
public static ReceiptStateResponseEvent start(Receipt ReceiptRequestPayload) throws Exception {
 ReceiptRulesState receiptRulesState = new ReceiptRulesState();
 return receiptRulesState.execute(ReceiptRequestPayload);

}
}
public abstract class AbstractRulesState <T, C, R, K> extends AbstractRulesFilterState<T, C> implements IRulesEngine<T> {
public R execute(T target) throws Exception{
 this.run();
 return this.getResponse();
}
}
public class ReturnRulesState
        extends
        AbstractRulesState <Order, OrderLine, Order, OrderQuantity> {
@Override
public void run() {
  
        runStateExecutorCompletionService(executorService);
}
}
4. Observer pattern
Observer pattern is used when there is one-to-many relationship between objects such as if one object is modified, its depenedent objects are to be notified automatically. Observer pattern falls under behavioral pattern category.
Implementation
Observer pattern uses three actor classes. Subject, Observer and Client. Subject is an object having methods to attach and detach observers to a client object. We have created an abstract class Observer and a concrete class Subject that is extending class Observer.
ObserverPatternDemo, our demo class, will use Subject and concrete class object to show observer pattern in action.
Step 1
Create Subject class.
Subject.java
import java.util.ArrayList;
import java.util.List;

public class Subject {
	
   private List<Observer> observers = new ArrayList<Observer>();
   private int state;

   public int getState() {
      return state;
   }

   public void setState(int state) {
      this.state = state;
      notifyAllObservers();
   }

   public void attach(Observer observer){
      observers.add(observer);		
   }

   public void notifyAllObservers(){
      for (Observer observer : observers) {
         observer.update();
      }
   } 	
}
Step 2
Create Observer class.
Observer.java
public abstract class Observer {
   protected Subject subject;
   public abstract void update();
}
Step 3
Create concrete observer classes
BinaryObserver.java
public class BinaryObserver extends Observer{

   public BinaryObserver(Subject subject){
      this.subject = subject;
      this.subject.attach(this);
   }

   @Override
   public void update() {
      System.out.println( "Binary String: " + Integer.toBinaryString( subject.getState() ) ); 
   }
}
OctalObserver.java
public class OctalObserver extends Observer{

   public OctalObserver(Subject subject){
      this.subject = subject;
      this.subject.attach(this);
   }

   @Override
   public void update() {
     System.out.println( "Octal String: " + Integer.toOctalString( subject.getState() ) ); 
   }
}
HexaObserver.java
public class HexaObserver extends Observer{

   public HexaObserver(Subject subject){
      this.subject = subject;
      this.subject.attach(this);
   }

   @Override
   public void update() {
      System.out.println( "Hex String: " + Integer.toHexString( subject.getState() ).toUpperCase() ); 
   }
}
Step 4
Use Subject and concrete observer objects.
ObserverPatternDemo.java
public class ObserverPatternDemo {
   public static void main(String[] args) {
      Subject subject = new Subject();

      new HexaObserver(subject);
      new OctalObserver(subject);
      new BinaryObserver(subject);

      System.out.println("First state change: 15");	
      subject.setState(15);
      System.out.println("Second state change: 10");	
      subject.setState(10);
   }
}
Step 5
Verify the output.
First state change: 15
Hex String: F
Octal String: 17
Binary String: 1111
Second state change: 10
Hex String: A
Octal String: 12
Binary String: 1010





Comments

Post a Comment

Popular posts from this blog

How to create Annotation in Spring boot

 To create Custom Annotation in JAVA, @interface keyword is used. The annotation contains :  1. Retention :  @Retention ( RetentionPolicy . RUNTIME ) It specifies that annotation should be available at runtime. 2. Target :  @Target ({ ElementType . METHOD }) It specifies that the annotation can only be applied to method. The target cane be modified to:   @Target ({ ElementType . TYPE }) for class level annotation @Target ({ ElementType . FIELD }) for field level annotation @Retention ( RetentionPolicy . RUNTIME ) @Target ({ ElementType . FIELD }) public @ interface CustomAnnotation { String value () default "default value" ; } value attribute is defined with @ CustomAnnotation annotation. If you want to use the attribute in annotation. A single attribute value. Example : public class Books {           @CustomAnnotation(value = "myBook")     public void updateBookDetail() {         ...
Post a Comment
Read more

Kafka And Zookeeper SetUp

 Kafka And Zookeeper SetUp zookeeper download Link : https://www.apache.org/dyn/closer.lua/zookeeper/zookeeper-3.8.3/apache-zookeeper-3.8.3-bin.tar.gz Configuration: zoo.conf # The number of milliseconds of each tick tickTime =2000 # The number of ticks that the initial # synchronization phase can take initLimit =10 # The number of ticks that can pass between # sending a request and getting an acknowledgement syncLimit =5 # the directory where the snapshot is stored. # do not use /tmp for storage, /tmp here is just # example sakes. dataDir =/tmp/zookeeper # the port at which the clients will connect clientPort =2181 4 char whitelist in command arguments 4lw.commands.whitelist =* Start ZooKeeper Server $ bin/zkServer.sh start Check zookeeper status dheeraj.kumar@Dheeraj-Kumar bin % echo stat | nc localhost 2181 stat is 4 character whitelisted argument  Check Kafka running status : echo dump | nc localhost 2181 | grep broker Responsibility of Leader in Zookeeper: 1. Distrib...
Post a Comment
Read more

Cache Policy

Cache policies determine how data is stored and retrieved from a cache, which is a small and fast storage area that holds frequently accessed data to reduce the latency of accessing that data from a slower, larger, and more distant storage location, such as main memory or disk. Different cache policies are designed to optimize various aspects of cache performance, including hit rate, latency, and consistency. Here are some common types of cache policies: Least Recently Used (LRU): LRU is a commonly used cache replacement policy. It evicts the least recently accessed item when the cache is full. LRU keeps track of the order in which items were accessed and removes the item that has not been accessed for the longest time. First-In-First-Out (FIFO): FIFO is a simple cache replacement policy. It removes the oldest item from the cache when new data needs to be stored, regardless of how frequently the items have been accessed. Most Recently Used (MRU): MRU removes the most recently accessed ...
Post a Comment
Read more